1. Field of the Invention
This invention relates to a mast assembly or derrick structure for drilling wells, such as oil or gas wells. It is particularly useful when installed on a floating drilling platform, such as a drilling vessel, but its use is not so limited, as many of its advantages are realized in land-based installations, or in mobile equipment for use on land.
2. Description of the Prior Art
Marine drilling rigs are known in which a mast or derrick is pivoted to a floating platform for swinging movements between a horizontal position, in which the floating rig is readily moved between drilling locations or sites, and a vertical position in which the drilling operation is performed. One such known rig is disclosed in U.S. Pat. No. 2,475,933 issued July 12, 1949, "Marine Drilling Rig", Woolslayer et al. Such masts are very heavy and require great power to raise them from the horizontal to the upright position.
If a hook assembly and traveling block guiding apparatus were to be added to the hoisting equipment, and if a vertical pipe rack and racker equipment were to be added to the mast or derrick, the weight of the assembly would become excessive, and it would, therefore, be impracticable to provide sufficient power to conveniently raise and lower the mast.